1. Field
This application relates to extractors used to pull a golf club shaft out of a golf club head.
2. Prior Art
Golf clubs have three main components; a shaft with a club head attached to its tip end and a grip covering its butt end. Heads are attached to shafts typically by adhesively securing the shaft into hole in a tubular extension of the head called a hosel. Sometimes it is necessary to extract a golf shaft from its head because the shaft has been damaged or because a golfer would like to try a different shaft in a head.
A desirable feature of a golf club shaft extractor is that its extraction force is applied symmetrically around the axis of the shaft. An asymmetrical force will apply a bending moment which can bend the shaft and cause damage: A bending moment in the shaft will also cause it to be held more tightly in its hosel hole than would otherwise be the case, because the moment urges the shaft to be moved out of alignment with the hole, causing a “binding” effect. Therefore, for any given set of conditions, an extractor which applies an extraction force which is more symmetrical with the shaft will result in less shaft bending and less extraction force than an extractor which applies a force which is more asymmetrical.
Another desirable feature is that the extractor can be used on a shaft which has a grip installed. A grip is normally cut and therefore ruined when removed. If a golfer extracts a shaft but later wants to use the shaft again, if the grip was removed to do the extraction, a new grip must be installed on the shaft, requiring extra time and expense.
An obviously desirable feature is that the extractor has a low manufacturing cost, and few parts, low weight, and relatively simple design help achieve this.
Two golf shaft extractors which use a piston and cylinder in their operation are described in U.S. Pat. No. 6,854,170 to D'Aguanno and U.S. Pat. No. 7,043,809 to Latiri. Both of these extractors use a bottle jack to apply a force to a golf club head while the shaft is held in a clamping device. The axis of the bottle jack is positioned away from the axis of the shaft, and therefore the jack's force vector is essentially parallel to, but not co-linear with, the axis of the shaft. This asymmetrical, off-center force results in a bending moment with respect to the shaft which is the product of the magnitude of the force times the displacement of the force vector from the shaft's axis. Both extractors use a fairly rigid frame to reduce the bending moment that is actually applied to the shaft by this asymmetrical force, but this frame adds cost and weight. The bending moment actually applied to the shaft, even though reduced, will still bend the shaft and add to the required extraction force.
Also, both of these inventions discuss the advantage of using a spring, compressed by the bottle jack, to allow smooth, hands-free extractor operation. This spring is beneficial because bottle jacks use a relatively incompressible fluid for the pressurized medium and therefore have a very high effective “spring rate” in their operation. In other words, absent a force applied to the handle of the bottle jack, even a slight outward movement of the jack's piston results in a significant decrease in hydraulic pressure and force applied by the jack. These extractors, without the use of a “softening” spring, would have an undesirably short effective extraction stroke, and would therefore require the operator to constantly apply a force to the jack's handle during operation to maintain the jack's extraction force.